Logging-While-Drilling (LWD) using a set of sensors at or near the drill bit to acquire data in real time has become an industry standard. This technique is used to direct high-angle and horizontal drilling to ensure cost-effective use of expensive drilling rigs. The collected data includes acoustic and rock mechanics, soil/rock density, gamma ray emission, nuclear magnetic resonance responses, and resistivity measurements. Also, Measurement While Drilling (MWD) tools provide essential information about the condition at the tip of the drill such as temperature, pressure, vibration, rotation speed of the drill bit, etc. to prevent tools failure. A robust and real-time data communication approach between the downhole drill head and the bore opening at the surface is used to transfer the data to the surface for logging. LWD/MWD data transmission is currently carried out by different techniques such as acoustic mud pulse telemetry, electromagnetic wireless links, and wired drill pipe technology. In acoustic mud pulse telemetry, the data is converted to pressure fluctuation which is then transmitted through the annular drilling mud fluid. Mud-pulse telemetry, however, provides a very low data rate and is not reliable. Electromagnetic wireless telemetry provides faster data transmission compared to acoustic mud pulse telemetry but is problematic in deep boreholes due to significant signal attenuation through the ground formation layers. Wired drill pipe technology utilizes electrical cables built into the drill pipe. This technology offers much faster data transmission, but is not commonly used as the required equipment is expensive and is prone to failure.
Outside the field of borehole drilling, there are known communication techniques using surface wave propagation on a single conductor transmission line (SCTL). To excite surface waves on a SCTL, a coaxial horn structure is normally used. However, the diameter of the horn-shape launcher is typically very large compared to the wavelength, resulting in large transverse electrical dimensions. These conventional launchers cannot be accommodated in standard boreholes and thus are not suitable for borehole communication.